The invention concerns a cylindrical window-type cage for a needle roller bearing.
A generic cage of the pre-cited type is known from DE-GM 18 29 610. This cylindrical window-type cage is made of a strip into which at first pockets are punched which are then deformed with a stamping tool so that when the metal strip is bent to form a cage, retaining projections are formed which prevent the needle rollers from falling out of the cage in outward direction. The retention of the needle rollers in inward direction is effected by the inclined walls of the crossbars. The material displacement which is initiated by the additional stamping process is such that material is displaced from the inside towards the outside so that after completion of the stamping process, the cage pocket, as seen in cross-section, ends in a roof-shape i.e., it tapers towards the outside.
A disadvantage of this is that, especially in bearing cages with a small diameter, the strong bending of the strip can lead to a clamping of the rolling elements in the pocket. A further disadvantage is that this shape of the pockets makes it more difficult to fill them with the rolling elements.
The object of the invention is therefore to provide a pocket shape which, particularly in the case of cages with a small diameter, permits a simple manufacturing of the bearing.
The invention achieves this object by the fact that in the unbent state of the cage strip, the surfaces of the crossbar walls of a pocket situated opposite each other are formed in the region of the retaining projections with three partial surfaces such that the first partial surfaces are parallel to a central vertical line and merge at their upper ends into inclined second partial surfaces pointing towards the center of the pocket, each of the second partial surfaces ending in a third partial surface which is likewise parallel to the central vertical line.
In this type of pocket configuration in which the retention of the rolling elements in inward direction is effected by the inclination of the crossbar walls and in outward direction by the retaining projections, the needle roller bearing cage is reliably guided on the partial surfaces situated in the middle and inclined towards each other. The configuration of the cross-section of the pockets according to the invention has the further advantage that, in small bearing cages which necessitate a very strong bending of the cage strip, no cracks and undesired deformations occur in the region of the pockets. A further additional advantage is that, due to the enlarged clear width of the pocket in upward direction, a more favorable elastic snapping-in of the needle rollers into the cage is possible.
The ratio of the diameter DL of the needle rollers to the pitch circle diameter DTK isxe2x89xa71:6. This means that the stamped pockets can be used particularly advantageously in cages having a small diameter i.e., in cages in which the original strip is subjected to a strong bending.
The manufacturing of a needle roller bearing cage is effected by the following steps:
punching a cage strip to form pockets defined by crossbars for the reception of the needle rollers,
introducing a tong-like stamping tool with two stamping jaws into adjoining pockets, pressure-loading said tool so that a displacement of material takes place such that, in the region of the retaining projections, opposing surfaces of the crossbar walls of a pocket are formed with three partial surfaces such that the two first partial surfaces are parallel to a central vertical line and merge at their upper ends into inclined second partial surfaces pointing towards the center of the pocket, each of the second partial surfaces ending in a third partial surface which is likewise parallel to the central vertical line,
cutting off a length of the cage strip to obtain a ratio of the diameter DL of the needle rollers to the pitch circle diameter DTK of greater than 1:6,
bending round the cage strip in a direction opposite to that of the material displacement and, if necessary, joining the abutting ends of the cage to each other.
Further, in the unbent state of the cage strip, the surfaces of the crossbar walls of a pocket situated opposite each other are formed in the region of the retaining projections with three partial surfaces such that the first partial surfaces are inclined relative to a central vertical line and point towards the center of the pocket while merging at their upper ends into second partial surfaces that are parallel to the central vertical line, each of the second partial surfaces ending in a third partial surface which is likewise inclined.
Due to this configuration of the pocket in the cage strip, the bent round cage can be filled with needle rollers without any problem from the inside, while the previously described cage shapes are mainly intended for the filling of the needle rollers from the outside. The manufacture of such a cage is effected in a manner analogous to the already described methods.
Finally, in the unbent state of the cage strip, the surfaces of the crossbar walls of a pocket situated opposite each other are formed in the region of the retaining projections with three partial surfaces such that the first partial surfaces are inclined relative to a central vertical line towards the center of the pocket and merge at their upper ends into likewise inclined second partial surfaces, each of the second partial surfaces ending in a third partial surface which is parallel to the central vertical line.
To conclude, the crossbars are profiled. As known, this means that the crossbars connecting the two side rings do not extend in one continuous horizontal line but are offset in upward or downward direction in a part of their axial length so that a horizontal portion is formed outside or inside the pitch circle, said horizontal portion being limited by two portions of the crossbar which extend at an angle to the bearing axis.
The invention will now be described more closely with reference to the following examples of embodiment.